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    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        f1();
        console.log(c);
        console.log(b);
        console.log(a);
        function f1() {
            var a = b = c = 9;
            console.log(a);
            console.log(b);
            console.log(c);
        }

        //相当于执行的下面的代码
        /*
            function f1() {
                 var a ;
                 a=b=c=9;
                          //相当于声明var a=9;b=9;c=9;  b和c直接赋值，没有var声明，当全局变量看
                         //集体声明 var a=9,b=9,c=9 ;这才是集体声明 var a=9 ; var b=9 ;var c=9

            console.log(a);   //9
            console.log(b);  //9
            console.log(c); //9
        }
          f1();
        console.log(c);  //undefined
        console.log(b);  //undefined
        console.log(a);  //undefined

         */
    </script>
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